Surface mount technology has become the technology of choice for electronics assembly in many countries throughout the world. This choice is due to the several benefits offered including the ability to produce higher density printed circuit boards, adaptability to automation, and lower weight. However, as the geometry of integrated circuitry packaging has been reduced greatly, there has been a significant decrease in throughput yield. In this regard, because fine pitch integrated circuits have closely spaced apart, fragile leads, there has been a significant increase in the number of foot-to-solder pad registration problems, and solder bridging during assembly, as compared with the larger size through-hole devices. Thus, significant numbers of printed circuit board assemblies are rejected and must be repaired or discarded.
Several attempts have been made to solve the above-mentioned registration and solder-bridging problems. For example, one such attempt includes using solder mask "dams" between the pads/lands where the leads of a surface-mount integrated circuit are to be soldered. The dam is designed to reduce the possibility of solder-bridging, though the technique adds cost and does not cause self-centering during component placement.
Another attempt to improve throughput yield is disclosed in U.S. Pat. No. 4,913,846 which discloses a three dimensional printed circuit board with grooved solder lands which facilitate greatly the self-location of the fine pitch leads during assembly. Such a technique also reduces coplanarity problems of the circuit component oftentimes having its lead distal ends not being disposed in a common plane. The solder grooves can thus permit a substantial deviation from coplanarity. Also, such grooves help overcome undesired and unwanted solder paste bridge problems during assembly.
While such a three dimensional circuit board has proven to be highly satisfactory, it would be highly desirable to have a method and apparatus for making such a board. In this regard, no manufacturer has been able to successfully manufacture molded printed circuit boards with recesses or grooves in commercial quantities in a suitable manner. For example, the conventional use of metal plating to form metallic traces within the molded printed circuit board grooves after molding has been insufficient to meet standard "peel" and "plug" tests as the nature of the material on the sides and bottom of such grooves causes the plating to be adhered weakly to the substrate surface. Thus, the metallic traces are easily separated from the substrate surface leading to unwanted and undesired electrical failures.
As to the problems relative to adhesion of metallic conductors to printed circuit boards refer to U.S. Pat. No. 3,666,549.
As to the problem, in general, of fixing metal to plastic material, the problem has also existed in the plating-on-plastic technology. See, for example, U.S. Pat. No. 5,073,237. In this form of a plating process, the problem has long existed of the metal separating from its underlying plastic substrate or part.
Therefore, it would be highly desirable to have a new and improved circuit board tool and method of using it to facilitate the manufacture of molded printed circuit boards with recesses or grooves in a relatively inexpensive manner. Moreover, such a method should result in a sufficiently strong bond between the plastic substrate and the metal substrate that metallization within the grooves can pass conventional peel and plug tests.
Another problem associated with molded printed circuit boards with recesses or grooves is that the formation of the grooves within thermoplastic substrates results in cold creep or shrinkage problems leading to misalignment of the grooves on the substrate.
Attempts also have been made to solve groove misalignment due to the cold creep problems, however, such attempts have proven less than totally satisfactory. In this regard, in order to help eliminate or at least greatly reduce the cold creep phenomenon long fibrous materials have been mixed with the plastic material to help eliminate or at least greatly reduce shrinkage. While such fibers help reduced shrinkage they cause the injection molding equipment to malfunction, thus resulting in low production yields due to unwanted and undesired equipment shutdown.
Therefore, it would be highly desirable to have a new and improved circuit board tool that can be used to produce a circuit board with grooves having metallized traces adhered firmly therewithin in a relatively inexpensive manner in acceptable substrate materials without causing unwanted and undesired failures. Moreover, such a circuit board tool should be capable of producing large quantities of printed circuit boards without the use of expensive injection mold tooling.